Radionuclide cardiac volumes: effects of region of interest selection and correction for Compton scatter using a buildup factor.

The effects of region of interest (ROI) selection and correction for Compton-scattered photons using a buildup factor on radionuclide left ventricular volumes calculated by the Links method were compared in 19 humans with contrast ventriculography and in phantoms. Three different methods of ROI selection were compared: a manual ROI, a second derivative ROI and a 50% count-threshold ROI. In phantoms without Compton scatter correction, volumes were overestimated by 30% (manual ROI), 20% (derivative ROI) and 1% (count threshold ROI). In subjects, results without Compton scatter correction were similar with overestimates of 50% (manual ROI) and 20% (derivative ROI) and an underestimate by 3% (count threshold method). Correction for Compton-scattered photons with the use of a phantom-derived buildup factor resulted in improved accuracy for the manual ROI (+15%) and the derivative ROI (0%). A 50% count threshold ROI following interpolative background subtraction allows the accurate calculation of cardiac volumes without the need for scatter correction, while a second derivative ROI method requires a correction for Compton scatter with the use of a buildup factor.

Four radionuclide methods for left ventricular volume determination: comparison of a manual and an automated technique.

This study compared the accuracy and reproducibility of three previously described and one new radionuclide method of measuring left ventricular volumes in 19 subjects using contrast ventriculographic volumes (n = 38, mean volume = 126.6 ml) as the gold standard. The four methods were compared using both manual and automated ROIs. For manual ROIs, the Links (189.7 ml, r = 0.85), Starling (183.2 ml, r = 0.77) and the new count ratio method (141.4 ml, r = 0.90) overestimated contrast volumes, while the Massardo method (122.5 ml, r = 0.91) provided accurate volumes. For the automated ROIs, we performed an interpolative background subtraction and used a 50% threshold of the highest count pixel to define the ventricular regions. The automated Massardo method severely underestimated the contrast volume (59.5 ml, r = 0.90), while the other automated methods yielded accurate volumes: Links (122.4 ml, r = 0.89), Starling (118.1 ml, r = 0.81) and the new count ratio method (125.0 ml, r = 0.90). The interobserver reproducibility of the automated methods was excellent (mean difference = 1%-4%) compared to the manual methods (2%-8%). Because no additional images, blood counting, attenuation, or decay correction were necessary, the manual Massardo method and the automated count ratio method are the simplest to perform. We conclude that automated determination of left ventricular volumes using the new count ratio method is rapid, accurate, reproducible and could readily be incorporated into routine clinical use.

Comparison of scintigraphic renal differentials using radiolabeled orthoiodohippurate and glucoheptonate.

Differential renal blood flow and parenchymal mass were compared in 50 pairs of scintigraphic studies performed on 44 patients. Background corrected total kidney counts were determined between 1 to 2 minutes following injection of I-123 or I-131 orthoiodohippurate (OIH), and at 1 to 2.5 hours after injection of Tc-99m glucoheptonate (GHA). The OIH and GHA differentials agreed within 5% in 36 studies (72%). When the OIH differentials were symmetric (45% to 55% in each kidney), agreement with the GHA results was complete (17 out of 17). By comparison, 42% (14 out of 33) of studies with asymmetric OIH differentials had a greater than 5% disparity from the GHA split function. Serum creatinine was elevated at the time of 9 out of 14 studies (64%) with OIH/GHA disagreement and 18 out of 36 studies (50%) with OIH/GHA agreement. Of the 14 studies with disparate OIH/GHA differentials, the GHA differential was more symmetric in 10 (71%). When different scinitigraphic measures of differential renal flow and parenchymal mass disagree, this is most likely due to the effects of asymmetric renal impairment rather than to those of global renal dysfunction.